Polarization analysis and corrections of different telescopes in polarization lidar

Abstract

Telescopes in polarization lidar often modify the input polarization of the return signal, such that the telescope may significantly impact the depolarization estimates of aerosol and introduce error to the polarization lidar measurements. The error cannot be corrected by a traditional calibration constant. We present a method to correct the polarization effect of the telescope. We analyze the polarization effect of a telescope on the basis of the Mueller formalism, and introduce an algorithm for correcting the depolarization parameter of aerosol. A Newton telescope and a Cassegrain telescope are often chosen as the receiver in lidar. Their polarization models are established, and the Mueller matrices are calculated. The components of these matrices are dependent on wavelength, incident angle of the incoming light, and surface properties. The polarization impact of the telescope in lidar can be calibrated by a parameter, and the effects of different telescopes are discussed. The polarization crosstalk induced by the Newton telescope is obvious. The depolarization parameters change greatly with coating and wavelength, and they are calculated and presented. Whereas the crosstalk of a Cassegrain telescope is much smaller, the error can reach the level of 10 −3 and can be negligible. The method presented in this paper could also be upgraded by taking into account all of the optical devices instead of only the telescope.

Assessment of lidar depolarization uncertainty by means of a polarimetric lidar simulator

“…The phase shift between the parallel (ϕ p ) and the perpendicular (ϕ s ) components, hereafter called retardance, is noted by This functional block, formed by the telescope and dichroic beam splitters, leads the received signal to the photomultipliers and, in case of multiwavelength lidar, separates the received signal by wavelength. In the same way as the emitting optics, M O can be described by a unique effective Müller matrix as follows: (Clark and Breckinridge, 2011;Di et al, 2015;Lam and Chipman, 2015) as in the case of the PollyXT lidars . This source of error has to be investigated further.…”

About the effects of polarising optics on lidar signals and the Δ90 calibration

“…Although the usefulness of a lidar with polarisation diversity had been realised early (Pal and Carswell 1973), the need for a complete description with the Müller-Stokes formalism was, to our knowledge, first expressed by Anderson (1989) but focused only on the atmospheric scattering process. Instrumental aspects including some error calculations have been included by Beyerle (1994), Cairo et al (1999), Biele et al (2000), Behrendt and Nakamura (2002), Reichardt et al (2003), Alvarez et al (2006), Del Guasta et al (2006, Hayman and Thayer (2009), Mattis et al (2009, Hayman (2011), Hayman and Thayer (2012), David et al (2013), Geier and Arienti (2014), Di et al (2015), and Volkov et al (2015). The errors mainly considered are the diattenuation of the receiver optics (see Sect.…”

“…For this we neglect the polarisation effects of lenses and of telescope mirrors with small incidence angles of the light beam (Seldomridge et al, 2006;Clark and Breckinridge 2011). Although not considered here, 90° folding mirrors as in Newtonian-type telescopes (Breckinridge et al, 2015;Di et al, 2015) and stress birefringence in windows and lenses or unfavourable coatings might cause severe polarisation effects. This requires further investigation.…”

Assessment of lidar depolarization uncertainty by means of a polarimetric lidar simulator

“…The polarization effects of telescopes with small incidence angles of the light beam are neglected in this work. This approximation is valid for Cassegrain telescopes, but possibly not for Newtonian telescopes with 90 • fold mirrors (Clark and Breckinridge, 2011;Di et al, 2015;Lam and Chipman, 2015) as in the case of the PollyXT lidars (Engelmann et al, 2016). This source of error has to be investigated further.…”